This invention relates to macromolecular monomers ("macromers" for brevity) of polyformals having a styryl, allyl, or acryloyl "head" (individually and collectively referred to herein as "vinyl functional") group at one end, and a terminal hydroxyl (OH) group at the other end. The term "polyformal" is used herein to refer, both, to homopolymers and copolymers. In copolymers, at least one of the monomers is an oxacyclic compound having a hetero ring containing two or more oxygen atoms, in which ring there is at most two substituted ring C atoms, and the 2-carbon atom, which is connected on each side to an O (oxygen) atom, is unsubstituted. The hetero ring is most preferably relatively small, having from 5 to 9 ring members, but may have as many as about 15 members if there are no more than 6 methylene --CH.sub.2 -- groups in an alkylene chain, and the remaining members are ethylene oxide --CH.sub.2 CH.sub.2 O)-repeating units. Polyformals of this invention are characterized as having at least two recurring units of a ring-opened oxacyclic monomer containing an oxymethyleneoxy --OCH.sub.2 O-- group. In this process, 1,3,5-trioxane does not form a useful polymer by itself, though it may be used as a comonomer to form copolymers with macromers of this invention, hence is not a cyclic formal as defined herein.
One of the major interests in the macromers of this invention is related to their being hydrophilic. They are at least partially water-soluble, that is, soluble in water in at least 5 parts by weight per 100 parts of water. The only commercially available water-soluble macromer is a low mol wt polyethylene oxide sold under the tradename Alcolac Sipomer.RTM. HEM-5, or HEM-10, the numbers indicating the average number of repeating units in a molecule. The choice of relatively small cyclic formals came about because it was expected that a polymer of such a compound would be water-soluble. Because those macromers derived from cyclic formals having more than 9 ring members with an alkylene chain having more than 6 methylene grorups, do not generally provide such hydrophilicity, they are of minor interest.
The polyformal macromer may be used to initiate block copolymerization with a ring-openable epoxide or gylcidyl ether, or with another cyclic formal monomer, to form a new macromer of block copolymer of cyclic formal-ether or cyclic formal-cyclic formal, respectively. Also, the polyformal macromer is copolymerizable through its head group with an olefinically unsaturated copolymerizable monomer. The copolymerization of the macromer with one or more conventional olefinic monomers generates a "polymacromer" with a hydrocarbon backbone having polyformal branches thus resulting in a graft or comb copolymer.
Conventional methods for the synthesis of graft copolymers primarily rely on polymerizing a monomer in the presence of a polymer which provides the backbone of the graft copolymer. However, neither the number of pendant chains, nor their length can be controlled, and the graft copolymer is contaminated with ungrafted polymer and homopolymers which should have been pendant chains. Moreover, conventional graft copolymerization is susceptible to generation of crosslinked chains.
The process of making the graft copolymer of macromer of this invention permits controlling (a) its predetermined molecular weight (mol wt) as well as the mol wt distribution of the pendant chains; (b) the balance of hydrophobic and hydrophilic properties, (c) the balance of its elastomeric and plastic properties, (d) its glass transition temperature (Tg), and the like, by tailoring the macromer. Most important is that this invention provides a unique process for designing copolymers of a cyclic formal and ethylenically unsaturated monomer. There is no satisfactory way of copolymerizing these monomers because of the difference in functionality between a cyclic formal and an ethylenically unsaturated monomer.
The macromer is formed in commercially acceptable yield by the cationic ring-opening polymerization of a cyclic formal in conjunction with (a) an alkenyl alcohol which functions as the generator of the propagating species, and (b) a cationic ring-opening catalyst such as an oxonium salt, or etherate of boron trifluoride. The alkenyl alcohol (referred to as the "propagator", because it functions as the `propagating species (OH group) generator` in the presence of a cationic initiator), if substituted, may have substituents which do not interfere with the initiation, propagation and transfer reactions which generate the macromer in a polymerization which has the characteristics of a living polymerization.
The macromer of this invention is formed by a onestep process which incorporates a vinyl functional head into the macromer during polymerization. An alkenyl alcohol functions as a propagating species, that is, the polymer chain propagates from the OH group of the alkenyl alcohol via polyaddition of a cyclic formal. As a result, each alkenyl alcohol molecule generates a polymer chain, and each such chain possesses the vinyl functional head group of the alcohol. This clearly distinguishes my process from conventional processes for preparation of a macromer in which processes a vinyl head group is incorporated after a polymer is preformed, via coupling reactions.
The textbook teaching is that polymerization of trioxane occurs by a direct initiation mechanism, which is proposed based on the experimental fact that the addition of a cocatalyst such as water is neither necessary nor useful. (see Kinetics and Mechanisms of Polymerization, by Frisch, K. C. and Reegan, S. L., Vol 2, Ring-Opening Polymerization, chapter titled "Cyclic Formals" by Furukawa and Tada pp 175, Marcel Dekker, 1969). They stated this was quite opposite to the case of cationic vinyl polymerization with a metal halide catalyst which itself has little activity without a cocatalyst like alcohol or water.
U.S. Pat. No. 3,652,465 to Takakura also teaches the use of water or alcohol in the reaction system must be avoided.
U.S. Pat. No. 3,595,812 to Kendall teaches the use of a carbonium or oxonium hexafluorophosphate catalyst for cyclic ethers, N-arylamino compounds, aromatic vinyl compounds and alkenes, particularly the 5-membered heterocycles containing 1 or 2 oxygen hetero atoms. The reaction is also preferably carried out under anhydrous conditions in the absence of a chain transfer or terminating agent, e.g. water, alcohols and amines.
Numerous other references teach the homopolymerization of formaldehyde, and of trioxane, and the copolymerization of trioxane with various cyclic ethers, for example, as taught in U.S. Pat. Nos. 2,951,059; 3,413,270; 3,883,450; 3,848,020; the '465 patent, and the like. U.S. Pat. No. 3,017,389 teaches the use of a small quantity of water, alcohol, and other compounds chain transfer agents for the polymerization of formaldehyde to control its mol wt. The implication was that the alcohol did not end up as part of the polymer chain.
In addition, the foregoing references were concerned with making a relatively high mol wt polymer for molding applications. Particularly with trioxane and its copolymers, they were produced with high mol wt, greater thana 100,000, for use as molding compounds which are highly insoluble in water, not to mention many commonly available solvents. Because, when alcohol was used is such polymerizations, it was used in very small quantity, it appeared likely that a large quantity of alcohol might terminate the polymerization, not participate in such a way as to provide a single terminal group at the head of a relatively low mol wt macromonomer, that is, one having a number average mol wt of less than about 100,000, and preferably less than 30,000. But no prediction could be made as to whether the polymerization would proceed without undesirable side reactions.
Thus, one would not expect a relatively large amount of alcohol to produce any especially beneficial results, particularly with respect to the formation of a macromer of controllable mol wt.
It should be recognized that, in copending patent applications Ser. Nos. 771,093 and 796,634, I have obtained allyl terminated, and styryl terminated macromers of polyethers by the cationic ring-opening polymerization of ethers using allyl alcohol and styryl alcohol, respectively, as the propagators, in a reaction involving the cationic ring-opening of an ether. However, there was little reason to assume the reaction would be effective in the polymerization of cyclic formals, which, because of the two hetero atoms, do not polymerize in a manner analogous to common ethers such as epichlorohydrin or ethylene oxide. Nor is there any known basis for predicting the properties which copolymerization of vinyl-functional polyformal macromers with olefinic monomers might contribute to copolymers formed with them. Nor was there any reason to believe catalysts taught by the prior art references to produce high mol wt polymers could also be used to make low mol wt macromers, some catalysts, such as oxonium salts, or etherate of BF.sub.3 being much more effective than others.
Particularly taught in U.S. Pat. No. 3,595,812 is that carbonium and oxonium hexafluorophosphate compounds which are catalysts for cyclic formals, are also catalysts for alkenes, so that, one who might consider the use of an ethylenically unsaturated alcohol as a modifier to prepare a polyformal macromer with terminal ethylenic unsaturation, would likely assume that the double bond would not survive conditions of cationic ring-opening. The fact that the double bond remains in tact, and the alkenyl alcohol still remains an effective propagator, though the reason for each observation is not clear, is one of the bases of this invention. I hypothesize that the presence of the hydroxyl (OH) groups might impair carbocationic polymerization of the ethylenically unsaturated groups.
It is to be noted that the macromers of this invention are formed by cationic ring-opening and not carbocationic polymerization, though both are classified as cationic polymerizations and may even use the same cationic initiator. The cationic ring-opening involves the opening of strained rings of cyclic monomers and the propagating species is an oxonium, sulfonium or ammonium ion; carbocationic polymerization involves substituted olefinic monomers where the propagating species is a carbenium ion.
With the emphasis on the essentiality of the OH propagating sites, the possibility that a vinyl group, and more specifically, an acryloyl, allyl, or styryl end group might survive the conditions of cationic ring-opening polymerization simply escaped notice. In view of the large number of olefinically unsaturated monomers which undergo polymerization (see the list in Carbocationic Polymerization by Kennedy, J. P. and Marechal, E., Table 3.6, pp 37 et seq., John Wiley & Sons 1982) the fate of the double bond of the propagator under such conditions seemed speculative. It is of particular commercial importance that the catalysts used herein produce the macromers of this invention in excellent yields generally above 80%, and usually at least 50%. Even among alkenyl alcohols, some vinyl headed alcohols will not survive under my conditions of cationic polymerization. For example, the ethylenically unsaturated group, such as 2-hydroxyethyl vinyl ether (CH.sub.2 .dbd.CHOCH.sub.2 CH.sub.2 OH), or, 4-hydroxybutyl vinyl ether, is an ineffective propagator. The vinyl ether group of the alkenyl alcohol does not survive under the conditions of cationic ring-opening polymerization of dioxolane and undergo carbocationic polymerization. As a result, the dioxolane polymers do not have an ethylenically unsaturated head group.
In addition to the carbocationic polymerization of the ethylenically unsaturated groups, there are two side reactions associated with cationic ring-opening polymerization of formals which appeared likely to vitiate the formation of the macromers of this invention. These side reactions are the hydride shift and transacetylization processes described by K. Weissermel et al in "Polymerization of Trioxane" Agnew. Chem. Intl. Ed., 6, 526-533 (1967).
Numerous catalysts are disclosed as being useful in ring-opening polymerizations, but there is no indication as to which might be used to provide a relatively low mol wt, nor is there any suggestion as to how to carry out the polymerization in the presence of an ethylenically unsaturated propagator so as to preserve the double bond. Though Takakura states that catalysts such as HClO.sub.4, BF.sub.3, FeCl.sub.3 and SnCl.sub.4 produce poly(1,3-dioxolane) ("poly(DOL)") ranging from liquid to solid, colored, low mol wt polymers, with too low activity to be considered satisfactory for practical, commercial use (see for example U.S. Pat. No. 3,652,465 to Takakura, col 1, lines 35-45), I find this is not generally so. For example, I find BF.sub.3 gives excellent results. Many other commonly available Lewis acid cationic ring-opening catalysts provide reasonably good results, though some are better than others.
From a study of the foregoing prior art, I concluded that there was no suggestion as to the role of a vinyl functional alcohol as a propagating species for the cationic ring-opening polymerization of cyclic formals; nor, that the vinyl head might survive conditions of cationic ring-opening polymerization; nor, that potential side reactions, hydride shift and transacetylation, would not vitiate the formation of the macromer; and, that the effect of a relatively large quantity of alcohol could not be predicted.